There is a pressing need to address the world's rising need for petroleum, and geologists continually search for methods to increase the availability of hydrocarbons, i.e. oil and gas, beneath the Earth's surface. In this search, various techniques may be used to generate data that is useful in oil and gas exploration, e.g. data that is useful for building and analyzing subsurface models of rock formations that could create petroleum reservoirs. These data are sometimes collectively referred to herein as “oil exploration data.”
Examples of oil exploration data may include: 1) geochemical data from potential source rock to quantify the nature of organic-rich rocks which may contain precursors to hydrocarbons; 2) data from potential reservoirs to assess their porosity and their permeability; 3) data indicating the thickness and extent of potential seals to quantify their effectiveness; 4) stratigraphic and/or structural feature data to identify the right juxtaposition of reservoir and seal such that hydrocarbons remain in subsurface traps; 5) thermal history data of the potential source rock (maturation) in order to make predictions of the amount and timing of hydrocarbon generation and expulsion; and 6) migration data to determine how hydrocarbons move from source to reservoir at the site. This oil exploration data may be used to identify one or more geographic search areas that may be further explored by test drilling and other techniques.
Oil exploration data may be gathered directly from a particular site. For example, oil exploration data may be generated from aerial surveys, gravimeter readings, magnetometer readings, stratigraphic records such as sample logs, driller's logs, time logs, electrical logs, radioactivity logs and acoustic logs, sedimentology studies, geochemical studies, and maps including contour, isopatch, cross-sections, and three-dimensional computer images.
Modern petroleum geologists frequently use seismology, and in particular reflection seismology, to generate oil exploration data at a particular location in the form of a “seismic survey.” A seismic survey involves creating shock waves that pass through subsurface rock layers and interpreting the waves that are reflected back to the surface. A shock wave is created by some means, e.g. a compressed-air gun (shooting pulses of air into the water for exploration over water), a thumper truck that slams heavy plates into the ground (for exploration over land) or explosives drilled into the ground or thrown overboard and detonated. The shock waves travel beneath the surface of the Earth and are reflected back by the various rock layers. The reflections travel at different speeds depending upon the type or density of rock layers through which they must pass. The reflections of the shock waves are detected by sensitive microphones or vibration detectors such as hydrophones for seismic surveys over water and seismometers for seismic surveys over land. The reflected signals are output onto a storage medium, for example, magnetic tape. Once the data is recorded, it can then be processed using specialist software which will result in processed seismic profiles being produced. Depending on the seismic survey technique used, the data may sometimes be used to create a three-dimensional image of the geology being surveyed. These seismic profiles and/or other data sets can then be interpreted to select possible hydrocarbon reserves. Once a prospective oil field is found, the location may be marked by GPS coordinates on land or by marker buoys on water. One aspect of investigating a site for a potential oil reservoir involves gathering as much exploration data as possible regarding the site and then analyzing that data. For example, in addition to seismic surveys conducted and recorded by or for the investigator, the investigator may perform one or more database searches to uncover oil exploration data relevant to the site that were generated by others.
The above methods help those in search of hydrocarbons to decide whether a particular tested location contains accessible hydrocarbon resources. However, countless locations remain untested. Searching for oil exploration data that was generated at a given site, or testing locations close to the site is a natural first step in acquiring further oil exploration data, and may provide the investigator with a useful set of information. However, depending on the particular potential reservoir, a local search of the present-day site may not be the optimal method of locating all relevant oil exploration data.